Photographic reproduction process



spasms PHO'E'GGRAPHEC REPRUDUCTIUN PRUCES No Drawing. Application August 25, 1955 Serial No. 530,638

2 Claims. (Cl. 96-48) This invention relates to a photographic reproduction process similar to that disclosed in the Yutzy and Yacltel U. S. Patent 2,675,313, granted April 13, 1954. In that process a substantially unhardened gelatino-silver halide emulsion layer is exposed to a subject and developed under conditions of gelatin tanning silver halide develop inent. Thereafter the moist developed emulsion layer is pressed against an absorbent surface to transfer a stratum of the less exposed and unhardened emulsion regions containing silver halide to the absorbent sheet. Various methods were disclosed for obtaining a dark image from the silver halide in the transferred emulsion stratum, for example, by incorporating an intensifying agent into the developing solution or by treating the developed emulsion layer with the intensifying agent subsequent to the development step. In that process it is frequently desirable to make more than one transfer print from the same developed emulsion layer and to i do so, the developed emulsion layer is repeatedly pressed against other receiving sheets. During this time and particularly when the emulsion has been exposed by the reflex method, tanning development of the whole emulsion layer is proceeding which tends to prevent the making of the desired additional prints, and whether the required additional prints are obtained, is dependent in part upon the speed with which the operator works during the period when the whole emulsion layer is being tanned. The mentioned patent proposes treating the developed emulsion layer with a sulfite solution to retard the tanning development of the less exposed emulsion areas and thus facilitate the making of the additional prints. In the Yutzy and Yackel U. S. patent application Serial No. 267,447, filed January 21, 1952, now U. S. Patent Q 2,716,059, granted August 23, 1955, another procedure is employed for this purpose. The development of the unhardened emulsion layer is carried out in the presence of both gelatin tanning and substantially nontanning silver halide developing agents with the result that the latter developing agent competes with the former and effectually prevents undue tanning of the less exposed areas of the emulsion layer.

We have discovered that greatly improved results are obtained in the process and the process is less dependent upon the operator if there is present at the surface of the absorbent receiving sheet to which the emulsion stratum is transferred, a mixture of (1) a silver halide fogging agent (that is, a compound which renders silver halide developable in the absence of light) such as thiourea, thioacetamide, dithioxamide, dithiobiuret, or thiosemicarbazide and (2) a compound which retards gelatin tanning in the presence of fogged silver halide and the gelatin tanning silver halide developing solution, for example, sodium formaldehyde bisulfite, sodium formaldehyde sulfoxalate, 2,4-dihydroxybenzoic acid, sodium tans benzene sulfinate, borophosphate, aminomethanesulfonic' acid, or borax. Accordingly, when the developed emul sion layer is pressed against the receiving sheet, the unexposed or less exposed regions of the emulsion adhere to the receiving sheet and at the same time the fogging agent commences to fog the unexposed silver halide and the gelatin tanning retarder, such as sodium formaldehyde bisulfite, tends to stop tanning development of the emulsion layer. Thus, the additional copies are readily obtainable from the same developed emulsion layer.

The method for preparing the receiving sheet containing the mixture of silver halide foggant and the gelatin tanning retarder is not especially critical. A paper stock,

such as a gelatin or melamine-formaldehyde resin moderately sized stock is coated with an aqueous solution of a suitable concentration of a mixture of the silver halide fogging agent and the gelatin tanning retarder, such that a coverage of the order of 50 milligrams per square foot of each compoundor less is obtained in the paper. If desired, the paper stock may be treated for this purpose in a tub-sizing bath containing the ingredients so as to apply them at a late stage of the paper-making operation or by a separate coating operation applied following the manufacture of the paper stock. It is, of course, desirable to carry out the coating operation by whatever method results in the compounds being deposited as near the surface of the paper as possible. In one series of operations, aqueous solutions containing 2.5 grams of thiourea and 5 to 20 grams of sodium formaldehyde bisulfite per liter deposited on a paper stock from about 40 to 200 milligrams per square foot of sodium formaldehyde bisulfite and from about 20 to 25 milligrams per square foot of thiourea. Aqueous coating solutions containing from about 0.5 to 5.0 grams of thiourea and about 1.0 to 5.0 grams of sodium formaldehyde bisulfite per liter will readily deposit on the paper about 5 to 50 mg. of thiourea and about l050 mg. of the bisulfite compound per square foot. Papers containing these amounts of thiourea and the bisulfite compound are particularly useful in the mentioned process. 'When the resulting coated papers were used as receiving sheets in the described processes, it was possible to obtain by the transfer procedure, as many as'six to nine good copies from a single developed emulsion layer compared to three to five when the uncoated paper receiving sheets were used.

In a similar manner, the other mentioned compounds which retard gelatin tanning silver halide development and fog silver halide which can be employed on the paper and used in the process. Suitable coverages of these compounds are also ofthe order of about 40 to 50 milli grams persquare foot of coating surface.

A representative method for taking maximum advantage of the improved receiving sheets of the invention is to provide a paper stock with an unhardened emulsion prepared by the methods described in the above lastmentioned Yutzy and Yackel invention and containing a mixture of gelatin tanning and substantially non-tanning silver halide developing agent such as 4-phenyl catechol and 4-methoxy-l-naphthol. The emulsion has a hardness of the order specified .by that invention. The emulsion is then exposed to a subject, preferably a line or halftone subject, by reflex methods followed 'by development with an alkaline solution such as a 4% sodium carbonate solution which may contain a small amount of a gelatin softening agent, such as urea. carried out for about 20 seconds at F. with the result that some silver density is obtained throughout the whole I Fatented Dec. 23, E

Development may be emulsion layer but considerably less tanning of the emulsion occurs in the less exposed regions. The exposed emulsion layer is then pressed against the receiving sheet of the invention and immediately thereafter is peeled off, leaving a thin relief print on the sheet composed of the transferred gelatin and silver resulting from the reduction of the transferred silver halide, as well as some silver sulfide resulting from the reaction of the thiourea on the receiving sheet with the transferred silver halide particularly in case thiourea has been used in the receiving sheet as the fogging agent. Thus, thiourea-causes the silver halide to become developable with the developing solution transferred to the sheet along with the stratum of gelatin and silver halide. When other silver halide fogging agents are used in the receiving sheet in place of thiourea such as those mentioned, the image density obtained may also be due to the reduction of the silver halide. Additional prints are prepared in the Same manner from the developed emulsion layer by merely rewetting it with the alkaline solution and pressing the emulsion layer against new receiving sheets.

As mentioned in the latter invention of Yutzy and Yackel, the tanning developing agents preferred for use in the unhardened emulsion layers are 3,4-dihydroxydiphenyl, 2,5-dihydroxydiphenyl and 2,3-dihydroxydiphenyl and the substantially nontanning silver halide developing agents preferably used with the tanning developing agents are N-methyl-p-arninophenolx-sulfonic acid, phydroxy-anilinomethane sulfonic acid, pyrogallol dimethyl ether, 8-hydroxy-a-naphthol and 4-methoxy-a-naphthol. Insofar as their solubilities permit, the mentioned gelatin tanning and substantially nontanning silver halide developing agents can either or both be employed in the silver halide emulsion layer or in the alkaline developer solution applied following the exposure step of the process. However, the best results are obtained when both developing agents are in the emulsion layer. In case the tanning developing agent is in the emulsion layer and the substantially nontanning developing agent is in the alkaline solution, the concentration of the latter developing agent should be of the order specified in the last-mentioned Yutzy and Yackel invention.

While the receiving sheets prepared as described and containing a mixture of silver halide fogging agent and This which layer does not interfere with the absorption characteristics of the sheet in the presence of alkali, yet the ink which is normally much less alkaline is repelled and the feathering of the ink impression is prevented. Suitable polymer solutions for coating the receiving sheet for this purpose are 0.5 to 0.35 percent ammoniacal solutions of a styrene-maleic anhydride (1:1) copolymer or the same concentration in ammonia solution of a methyl methacrylate-methacrylic acid (1:1) copolymer. Ammonia solutions of the same concentration of the following polymers are also useful for this purpose: acrylic acid-acrylonitrile-butyl acrylate tripolymer (14.9-61.5- 23.6 mol percent respectively) or (7-62.9-30.1 mol percent respectively); vinyl alcohol-vinyl acetate-vinyl butyral-vinyl phthalate copolymer (19.1-08-606-195 mol percent respectively).

If desired, rather than coating these polymeric materials in a separate operation upon the receiving sheet carrying the silver halide fogging agent and gelatin tanning retarder, the polymeric materials may be added to the solution of fogging agent and tanning retarder and the single solution coated upon the paper base to provide the anti-feathering properties.

Other materials very useful for alleviating feathering are methylacrylato chromic chloride, stearato chromic chloride and Aquapel S380 (the ketoketone, stearoyl hexadecyl ethenone, in water-dispersible form, Hercules Powder Co.). Suitable aqueous coating compositions for coating paper with these materials are for example 0.9 gm. of stearato chromic chloride, 2 grams thiourea, 2 grams of sodium formaldehyde bisulfite per liter; and 8.0 grams Aquapel 8-380, 0.86 gram thiourea and 1.6 grams sodium formaldehyde bisulfite per liter.

In addition to the use of ordinary paper stock for coating with the silver halide fogging agents and gelatintanning retarders, a translucent stock such as prepared in the Griggs et a1. U. S. patent application Serial No. 336,015, filed February 9, 1953, may be employed. This translucent stock comprises a fibrous cellulosic base such as a paper or cloth stock which has been impregnated with polymerized -methylstyrene. An aqueous coating composition suitable for application to the translucent base is 40.0 grams thiourea, 50 grams urea, 2 grams Duponol ME (a fatty alcohol sulfate surfactant). This solution will readily deposit about 70 mg. thiourea, mg. urea and 3.5 mg. Duponol ME per square foot of surface. The essential component of the solution is the thiourea although the surfactant aids in obtaining a uniform coating on the translucent base. Also, both the surfactant and the urea improve the quality of the colloid image transferred to the base from the exposed and developed emulsion layer. The coating solution may in addition contain one of the indicated gelatin tanning re tarders such as sodium formaldehyde bisulfite in quantity sufiicient to obtain about 10 to 50 mg. per square foot of coating surface.

The translucent receiving sheet is used in the manner previously described, the unhardened emulsion layer being exposed, developed with alkaline solution, pressing the developed emulsion against the coated translucent base and at once peeling the two elements apart to leave a black gelatin relief image adhering to the translucent base. The resultant image on the translucent base can then be used as an ordinary subject in making additional copies by printing with transmitted light onto a light-sensitive element such as a silver halide emulsion layer or a diazo sensitized sheet.

We have indicated above that a surfactant such as Duponol ME present on the receiving sheet improves the quality of the prints obtained. This may be due in part to more of the emulsion transferring tothe receiving sheet than would otherwise be the case. Similarly it has been found that if surface active agents are incorporated into the alkaline solution used for initiating development of the exposed emulsion layer, a similar improvement in quality of the prints is obtained, presumably by the same mechanism. Some of the useful surface active agents are Duponol ME, Kreelon (a sodium alkylarylsulfonate, Wyandotte Chemical Corp.), Atolene NR (a sulfonated fatty acid, Dexter Chemical Co.), Sorbit P (an alkylarylsulfonate, Alrose Chemical Co), Aerosol OT (dioctyl sodium sulfosuccinate, American Cyanamide Co.), Size Aid (trisodium maleopimarate, Hercules Powder Co.), Dry Pexol (sodium salt of a carboxylated polymer, Monsanto Chemical Co.). Other useful surface active agents will occur to those skilled in the art.

What we claim is:

l. A paper base having thereon a mixture of from about 5 to 50 milligrams of thiourca per square foot and from about 10 to 50 milligrams of sodium formaldehyde bisulfite per square foot.

2. A method of photographic reproduction which comprises exposing to a subject a substantially unhardened gelatino-silver halide emulsion layer containing a gelatin tanning silver halide developing agent, developing the exposed emulsion layer with an alkaline solution to obtain a hardened gelatin and silver image in the region of most exposure and substantially unhardened gelatin and silver halide in the less exposed regions of the emulsion layer, pressing the developed emulsion layer while moist with the alkaline solution, against an absorbent surface having thereon a mixture of thiourea and sodium formaldehyde bisulfite, thereby causing only the unexposed regions of the emulsion layer to adhere to the absorbent surface and the silver halidethereon to be converted to a black image, and separating said receiving sheet and emulsion layer to transfer only a stratum of the unexposed region of the sheet.

emulsion layer containing the black image to the receiving References Cited in the file of this patent UNITED STATES PATENTS 

2. A METHOD OF PHOTOGRAPHIC REPRODUCTION WHICH COMPRISES EXPOSING TO A SUBJECT A SUBSTANTIALLY UNHARDENED GELATINO-SILVER HALIDE EMULSION LAYER CONTAINING A GELATIN TANNING SILVER HALIDE DEVELOPING AGENT, DEVELOPING THE EXPOSED EMULSION LAYER WITH AN ALKALINE SOLUTION TO OBTAIN A HARDENED GELATIN AND SILVER IMAGE IN THE REGION OF MOST EXPOSURE AND SUBSTANTIALLY UNHARDENED GELATIN AND SILVER HALIDE IN THE LESS EXPOSED REGIONS OF THE EMULSION LAYER, PRESSING THE DEVELOPED EMULSION LAYER WHILE MOIST WITH THE ALKALINE SOLUTION, AGAINST AN ABSORBENT SURFACE HAVING THEREON A MIXTURE OF THIOUREA AND SODIUM FORMALDEHYDE BISULFITE, THEREBY CAUSING ONLY THE UNEXPOSED REGIONS OF THE EMULSION LAYER TO ADHERE TO THE ABSORBENT SURFACE AND THE SILVER HALIDE THEREON TO BE CONVERTED TO A BLACK IMAGE, AND SEPARATING SAID RECEIVING SHEET AND EMULSION LAYER TO TRANSFER ONLY A STRATUM OF THE UNEXPOSED REGION OF THE EMULSION LAYER CONTAINING THE BLACK IMAGE TO THE RECEIVING SHEET. 